You can use a quick field test to check for prussic acid in forage

Annual forages are a great resource for producers, but those using sorghums or sudangrass species always need to keep the risk of prussic acid in the back of their mind. At any time of year, young shoots of sorghum species contain prussic acid, which is why recommendations are to allow ample growth (15-18 inches on new plants) before grazing. When ingested by livestock, the cyanide is released can quickly cause lethal results when consumed in high amounts.